The present invention relates to heating units and pertains particularly to an electrical heating unit having both weight responsive and thermally responsive control for the circuit.
Electrical heating units for heating coffee pots and the like and having a pressure responsive switch responsive to a coffee pot having a predetermined amount of contents for activating the circuit have been known for some time. Such heating units have circuits which are activated only when a predetermined minimal amount of water or coffee or other liquid is contained within the pot. When the contents of the pot falls below a certain minimum amount, such as one cup or the like, the circuit will be interrupted. Such heaters are relatively safe and trouble free when properly used. However, it has been found that when a person desired to heat less than the minimal amount of liquid necessary to activate the circuit, the tendency is to put a weight such as a book or the like on the pot to weight it down. Should the individual forget the unit and the pot runs dry, the unit could overheat and cause a fire.
It has also been found that an individual may have a tendency to use a pot or container that is not properly suited to use on the heating unit. The container, for example, may have sufficient weight to activate the circuit without the presence of liquid therein. This again can cause a hazardous situation. Other containers such as cups not suitable for heating are also sometimes used. This can also be hazardous.
Accordingly, it is desirable that a heating unit be available which discourages the use of other than an appropriate container and also is responsive to cut off the unit should the weight responsive control fail.